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Re: flight stroke (pretty short)



David Marjanovic wrote:

> > The elongate femoral feathers may prove to
> > be gliding surfaces in Jehol Deinonychosaurs,
> > though.
> 
> Would require the ability to sprawl.

Hehehe, no that wasn't what I was implying. If the
femur were held parallel to the presacral column, the
feathers could fold or splay to the sides. Shouldn't
be long before we can confirm or deny this.  
 
> Just a little, I meant, so that not so much lift is
> produced in front of the
> cg. But I was thinking too much of an animal with a
> full patagium, like a
> gliding squirrel, which is out of place here :-)

Ok, I see what you're saying now. It does make sense.
However, you loose some of the lift provided by that
patagium by allowing air to spill out more rapidly in
front. I'm trying to think of a way to balance the
body AND keep your surface area maximized.  
 
> I remember having read somewhere that "Ulla Norberg
> (1985) has shown how
> slow flaps might overcome the problem" of the
> glide-fly transition, "but
> there is no living animal that glide-flaps this way"
> or something like that,
> I'll look up the refs. Maybe you are reinventing
> that :-) -- my prime
> objection is: how does the animal get the idea
> (consciously, by instinct,
> however) of flapping?

No matter the scenario, you run into that very
problem. Maybe gliders sense when their bodies are out
of balance, and wave their arms in an attempt to
steady themselves - The same way you would if you were
trying to balance at the end of a diving board on your
tiptoes. Exaptation clearly happens, but what makes
the animal suddenly decide to use an organ in a novel
way? Hell if I know. I doubt many genes would need to
be altered in order to cause a weak repetitive motion
of the arms in any case, but I do think it would be
atypical for the flight stroke to evolve from scratch.
      

> No idea how much lift (or drag, for that matter)
> Archie's tail could produce. Certainly easy to 
> test, but I don't know if anyone has done it.

It looks like a control surface to me, with that
distal fan at the end. The way modern birds use their
retrices indicates this was precisely the purpose.
Feathertail gliders also do this I've read. I'm not
sure how Archie steered with it, but if twisting was
involved, the weight of the tail would be more
apparent because of the loss of air to one side....I
*think.* I also think it's pretty strange that all of
the flying groups seem to have convergently reduced
their tail length, and that those who didn't are more
terrestrial (like pheasants, and peacocks)

Re: to Graydon:

> One is that in living birds, the good gliders are
> all highly derived forms; the basic bird wing, as 
> per the bracket between tiamous and chickens, is a >
high output system for energetic flight. This is not
> something one would expect a glider to evolve
> into.

Well, I'm not so sure modern birds are a good example
because of their flight adaptations - even in those
species that are only gliders.     

> To add some comments about the basic bird wing (as
> opposed to the basic
> neornithine wing), I wonder why there are no real
> remiges on the upper arms,
> just tertials to fill in the gap between the remiges
> and the body. Such a
> gap is not seen in any certain glider I know of.
> It's not sure whether
> *Archaeopteryx* or *Caudipteryx* even had tertials.

Yes, that IS odd. Femoral feathers might have filled
this gap, or maybe the humerus was held closer to the
body than we think during gliding? This would orient
the feathers further posterior, near the center of
gravity. Pulling the wings forward from that position
to land might also be a way in which the flight stroke
evolved. I can think of several gliders that have
evolved wings or patagia near the CoG. The Draco
lizard, and *Sharovipteryx.* 

Cheers,
Waylon Rowley

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